The reduction in noise pollution in places of residence is a widespread concern and quietness appears to be the first criteria of choice in the search for housing. Furthermore, noise is the first ground for dissatisfaction when the occupants of apartments talk about their housing.
The clack of shoes on the flooring of one floor of a place of residence when walking, the dropping of an object or the moving of furniture are some examples of activities which are a source of noise pollution for the occupants of the lower floor. These various impact noises cause the vibration of the flooring, which is transmitted through the whole of the structure and especially in the ceiling of the lower floor, and which then radiates in the ambient air of the latter.
Rigid coverings, and especially parquet or tiled floors, contribute as components of the floor to the transmission of impact noises, and therefore to the acoustic comfort of the occupants of places of residence. Generally, the quality of the sound insulation against the impact noises required for parquet flooring is measured by the value of the expression ΔLw (expressed in decibels or dB) in accordance with the EN ISO 717-2 standard.
Parquet is a wood-based floorcovering, of which the components of rectangular shape (denoted by the terms strips, boards or panels) may be laid according to various processes over the surface of the underlying support. The latter is usually a concrete slab, rough or covered with a levelling compound. The support may also be, in the case of renovating an existing dwelling, another material such as tiling, metal or else a wood-based floor.
Among the various installation processes, parquet known as bonded parquet is often used due to an advantageous mechanical and dimensional stability, in the face of temperature and hygrometry variations in the surrounding atmosphere. These variations may lead, over time, to an expansion of the components of the parquet which risks resulting—in extreme situations—in the delamination and/or lifting up of the boards. This mechanical stability is often evaluated by a measurement of the delamination strength of strips of parquet in a direction perpendicular to the surface of the support.
The laying of such parquet requires a prior step of applying and/or spreading the adhesive over the support.
A notched spatula applicator denoted hereinafter by the term “spatula No. 4,” which is illustrated as a front view in FIG. 3, is well known in the art.
According to FIG. 3, the “spatula No. 4” 1 comprises a spatula 2 which is in the strict sense of the word a wide and flexible blade of rectangular or trapezoid shape, in general metallic and usually made from stainless steel, and which is equipped over the entire length of its working edge 2c with a fine serration. The spatula 2 is directly attached to a handle 3, for example made of wood. The fine serration of the spatula 2, represented schematically in FIG. 3, results from the juxtaposition of notches (or recesses) 4 which each have the shape of a triangle of height 3.8 mm and of base 4.2 mm, and which are spaced 4.8 mm apart.
The spatula No. 4 is held in the hand by the operator (or layer) in order to use it. The latter works by leaning on the support by means of his knees and optionally one hand. From a container (for example a pot) he removes, using the spatula, a certain amount of adhesive which he deposits on the support. While pressing the working edge of the flexible blade against the surface of the support, he then handles the spatula so as to give the amount of adhesive the form of a substantially homogeneous layer, constituted of parallel and essentially contiguous filaments.
The strips of parquet are, after a waiting period of a few tens of minutes, applied to the thus coated support.
Such a process, in which the adhesive is applied in the form of a substantially homogeneous layer onto the support is denoted in the trade by the terminology of “continuous bonding”.
The spatula No. 4 from FIG. 3 however forces the operator to remain on his knees during the entire time necessary to carry out his task, which leads to discomfort and pain when working, most particularly for laying coverings over vast surfaces.
Notched spatula applicators have been developed for the purpose of overcoming this drawback. These applicators are devices in which the notched spatula is indirectly connected, especially via a rod, to gripping means, which enable it to be handled by the operator in the standing position. Such applicators are, for example, described in international Application WO 02/100555 and in U.S. Pat. No. 3,611,470, U.S. Pat. No. 3,803,662 and U.S. Pat. No. 4,982,470. These devices are used for applying adhesive according to the continuous-bonding process.
The process of continuous bonding, carried out in particular using a notched spatula tool such as the spatula No. 4, is very widely used by the professionals for laying parquet, due to the particularly advantageous mechanical and dimensional stability of the laid parquet that it provides, and also for its ease and rapidity of implementation. However, the quality of the sound insulation to the impact noises provided by parquet bonded according to this process is very inadequate.
Another process for laying parquet that is used in practice is the process known as “bead bonding”. According to this process, the adhesive is contained in a sealed container (or cartridge) placed in a gun, and is deposited onto the surface of the support to be coated by extrusion through a cannula (or nozzle), in the form of a bead, the diameter of which is defined by the diameter of the nozzle, generally between 3 and 15 mm. These beads are positioned by the fitter in a substantially parallel manner on the surface of the support and evenly spaced apart by around 10 to 20 cm. This process is especially used for compensating for the presence of defects in the flatness of the support to be coated.
Various processes for bead bonding that aim to improve the acoustic comfort of places of residence are already known in the prior art.
Thus, French Patent Application 2710675 describes a process that consists in placing, between the beads of adhesive (separated by 5 to 20 cm), seals that limit the squashing of the beads during laying of the parquet, so as to make between the parquet and the support an air space that provides sound and thermal insulation. However, the laying of these seals complicates and further lengthens the fitting time.
French Patent Application 2751357 describes a process comprising the application, to the support, of an insulating sublayer that has a plurality of recesses intended to receive the beads of the adhesive for attaching the parquet. Such a sublayer however involves a very significant additional cost.
French Patent Application 2787116 describes a process for depositing, in beads, a bonding material made up of a binder and comprising less than 5% of polymer or rubber grains having a size of around 1 to 6 mm as a bulk additive.
The process of bead bonding, which requires a cartridge placed in a gun, and which is carried out in these 3 patent applications, has several drawbacks relative to the continuous-bonding process. As a result it has a lower dimensional stability of the laid parquet, with a lower delamination strength. Due to the time necessary to extrude beads via the cannula of the cartridge, it takes longer to carry out; it is also more expensive. These drawbacks are even greater when the surface area of parquet to be laid is larger.